It has been found to be very useful to have enzymes in dishwashing detergent compositions because enzymes are very effective in removing food soils from the surface of glasses, dishes, pots, pans and eating utensils. The enzymes attack these materials while other components of the detergent will effect other aspects of the cleaning action. However, in order for the enzymes to be highly effective, the composition must be chemically stable, and it must maintain an effective activity at the operating temperature of the automatic dishwasher. Chemical stability, such as to bleach agents, is the property whereby the detergent composition containing enzymes does not undergo any significant degradation during storage. Activity is the property of maintaining enzyme activity during usage. Front the time that a detergent is packaged until it is used by the customer, it must remain stable. Furthermore, during customer usage of the dishwashing detergent, it must retain its activity. Unless the enzymes in the detergent are maintained in a minimum exposure to moisture and water, the enzymes will suffer a degradation during storage which will result in a product that will have a decreased activity. When enzymes are a part of the detergent composition, it has been found that the initial water content of the components of the composition should be as low a level as possible, and this low water content must be maintained during storage, since water in the alkaline product will deactivate the enzymes. This deactivation will cause a decrease in the initial activity of the detergent composition.
After the detergent container is opened, the detergent will be exposed to the environment which contains moisture. During each instance that the detergent is exposed to the environment it could possibly absorb some moisture. This absorption occurs by components of the detergent composition absorbing moisture, when in contact with the atmosphere. This effect is increased as the container is emptied, since there will be a greater volume of air in contact with the detergent, and thus more available moisture to be absorbed by the detergent composition. This will usually accelerate the decrease in the activity of the detergent composition. The most efficient way to keep a high activity is to start with an initial high activity of enzyme and to use components in the dishwashing composition which do not interact with the enzyme or have a low water affinity which will minimize any losses in activity as the detergent is being stored or used.
Powdered detergent compositions which contain enzymes can be made more stable and to have a high activity, if the initial free water content of the detergent composition is less than about 10 percent by weight, more preferably less than about 9 percent by weight and most preferably less than about 8 percent by weight. Furthermore, the pH of a 1.0 wt % aqueous solution of the powdered detergent composition should be less than about 11.0 more preferably less than about 10.6, and most preferably less than about 10.3. This low alkalinity of the dishwashing detergent should maintain the stability of the detergent composition which contains a mixture of enzymes, thereby providing a higher initial activity of the mixture of the enzymes and the maintenance of this initial high activity.
A major concern in the use of automatic dishwashing compositions is the formulation of automatic dishwashing compositions which have a low alkalinity and can operate at a high temperature while maintaining superior cleaning performance and dish care. The present invention teaches the preparation and use of powdered automatic dishwashing compositions which are phosphate containing and have superior cleaning performance and dish care and are used at operating temperatures of 100.degree. F. to 140.degree. F.